Fingerprint sensing and matching is a reliable and widely used technique for personal identification or verification. In particular, a common approach to fingerprint identification involves scanning a sample fingerprint or an image thereof and storing the image and/or unique characteristics of the fingerprint image. The characteristics of a sample fingerprint may be compared to information for reference fingerprints already in a database to determine proper identification of a person, such as for verification purposes.
A particularly advantageous approach to fingerprint sensing is disclosed in U.S. Pat. No. 5,963,679 to Setlak et al., assigned to the assignee of the present invention, and the entire disclosure of which is incorporated herein by reference. The fingerprint sensor is an integrated circuit sensor that drives the user's finger with an electric field signal and senses the electric field with an array of electric field sensing pixels on the integrated circuit substrate. Such sensors are used to control access for many different types of electronic devices such as computers, cell phones, personal digital assistants (PDA's), and the like. In particular, fingerprint sensors are used because they may have a small footprint, are relatively easy for a user to use, and they provide reasonable authentication capabilities.
U.S. Published Patent Application No. 2005/0089203 also to Setlak, assigned to the assignee of the present invention, and the entire disclosure of which is incorporated herein by reference, discloses an integrated circuit biometric sensor that may sense multiple biometrics of the user, and that is also adapted to either a static placement sensor or a slide finger sensor. A slide finger sensor includes a smaller sensing surface over which the user's finger is slid. The images collected during the sliding process may be collected for matching, such as for authentication, or may be used for navigation, for example,
U.S. Published Patent Application No. 2005/0078855 to Chandler et al., assigned to the assignee of the present invention, and the entire disclosure of which is incorporated herein by reference, discloses a finger sensor used for navigation. More particularly, a processor is coupled to the finger sensing area to generate a plurality of menu items on a display, and for scrolling an indicator along the menu items based upon static placement of a finger adjacent a selected portion of the sensing area.
U.S. Published Patent Application No. 2001/0017934 to Palonieme et al. discloses a cellular telephone including a finger sensor for sensing surface the relief areas of human skin, and a movement detector for detecting movement of skin across the sensor. A user interface is responsive to the finger sensor to perform navigation functions.
U.S. Published Patent Application No. 2005/0012714 to Russo et al. also discloses a finger sensor used in a portable electronic device that translates a difference between first and second positions on the sensor into a plurality of sets of signals. Each set of signals may be used to emulate the signals generated by an input device, such as a steering wheel, a mouse, a joystick, a navigation bar, a scroll wheel, and a pressure sensitive button.
U.S. Published Patent Application No. 2006/0088195 to Tykowski et al., assigned to the assignee of the present invention, and the entire disclosure of which is incorporated herein by reference, discloses a finger sensing device including a finger sensing area to receive a user's finger moved in a sliding motion, and a controller cooperating with the finger sensing area for generating successive image samples at least some of which are separated by different time intervals. The controller may generate finger movement signals based upon the successive image samples and the different time intervals. The controller may generate a plurality of repeating groups of ratio-metrically related image samples based upon the different time intervals. The reduced number of image samples may provide greater processing efficiency and reduced power consumption.
Image-to-image correlation for finger sensing is a well known method for image alignment to those skilled in the art. The process of correlation compares two images and computes a displacement in X and Y between them. However, simply setting thresholds and examining scores from a single correlator may not always be sufficient to make an accurate assessment of motion between two time varying images. In other words, correlators may have a significant shortcoming in that they make mistakes. These mistakes can cause havoc in a finger sensing system where the correct answer is needed, and when no answer may be better than a bad answer. For example, in a finger sensing navigation subsystem used as a pointing device, a single miscorrelation can cause the cursor to jump wildly on the screen.